Leukocyte adherence to endothelial cells is an early and rate-limiting event in the overall pathogenesis of ischemia-reperfusion induced injury to the intestinal microvasculature. The propensity for leukocytes to adhere to microvascular endothelium and subsequently emigrate from the blood stream is determined by the balance between adhesive forces that are generated by membrane glycoproteins on the surface of both leukocytes (CD11/CD18) and endothelial cells (ICAM-1), and the hydrodynamic dispersal forces (e.g., erythrocyte velocity) that tend to sweep leukocytes away from the endothelial surface. The overall objective of the work outlined in this proposal is to determine how variations in shear forces, over a range that is predicted to occur during ischemia and reperfusion, influence leukocyte-endothelial cell adhesive interactions in cat mesenteric venules. The relationships among leukocyte rolling velocity, adherence and venular hemodynamics (blood flow, erythrocyte velocity, wall shear rate) will be defined in normal venules and in venules exposed to a proinflammatory stimulus (PAF or LTB4). The latter studies will allow us to determine how an increase in leukocyte adhesiveness, as occurs during ischemia- reperfusion, alters the influence of shear forces on leukocyte-endothelial cell interactions. Studies are also proposed to define the relative roles of the leukocyte and endothelial cell adhesive glycoproteins in shear rate- dependent leukocyte adherence and rolling. Immunoneutralization of CD11/CD18 and ICAM-1 will be achieved using specific monoclonal antibodies. The role of neutrophil derived oxidants (superoxide and hydrogen peroxide) will also be assessed using the antioxidant enzymes, superoxide dismutase and catalase. Another major objective of this project is to determine whether venular wall shear rate influences the ability of a leukocyte to emigrate from the vasculature in response to specific proinflammatory stimuli. The results derived from all of the studies outlined in this application should extend current knowledge regarding the leukocyte- endothelial cell adhesive interactions that occur during ischemia- reperfusion and how these interactions ultimately contribute to the microvascular dysfunction that is observed following reperfusion of ischemic tissues.